1. Field of the Invention
The present invention relates to a projection type display apparatus using a plurality of light valves and, more particularly, to a constituent part mainly including a synthesizing optical system for synthesizing beams projected from respective light valves in the projection type display apparatus.
2. Related Background Art
Such projection type display apparatus as a color projector are used as large-screen image display apparatus and the projection type display apparatus of this type are classified under a method called a single plate method for directly magnifying and projecting a color image and a method called a three plate method for synthesizing images of the three primary colors R (red), G (green), B (blue) and projecting the synthesized image. The three plate method requires more complex apparatus structure than the single plate method, but is easier in color adjustment and more advantageous in color reproduction, resolution, and so on than the single plate type. The three plate method is thus popularly employed in imagery equipment or the like.
An example of such three plate method projection type display apparatus is shown in FIG. 18. White source light including the respective colors R, G, B, emitted from a light source not illustrated, is split into two directions of respective polarization components by polarization beam splitter 11xe2x80x2. Only R light in the component reflected by the polarization beam splitter 11xe2x80x2 is transmitted by red transmitting dichroic filter 52 to enter light valve 12R for R signal. The R light is modulated to light having an image signal of R signal and this light travels again through the red transmitting dichroic filter 52 to enter the polarization beam splitter 11xe2x80x2. Only the signal component is extracted from the light in the polarization beam splitter 11xe2x80x2 to be outputted. On the other hand, the G light component of the polarized light component transmitted by the polarization beam splitter 11xe2x80x2 is reflected to branch off by green reflecting dichroic mirror 51 to enter light valve 12G for G signal. The G light is modulated to light having an image signal of G signal to be reflected. Then the light is again reflected by the green reflecting dichroic mirror 51 to enter the polarization beam splitter 11xe2x80x2, in which only the signal component is extracted to be outputted. The B light component in the light transmitted by the green reflecting dichroic mirror 51 is extracted by blue transmitting dichroic filter 53 to enter the light valve for B signal. The B light is modulated to light having an image signal of B signal to be reflected. Then the light travels again through the blue transmitting dichroic filter 53 and then through the green reflecting dichroic mirror 51 to enter the polarization beam splitter 11xe2x80x2, in which only the signal component is extracted to be outputted. As a result, the signal components R, G, B are synthesized by the polarization beam splitter 11xe2x80x2 and the synthetic light is outputted to be enlarged and projected through projection lens 14 onto a screen not illustrated. Unwanted light components are outputted along the direction of the source light, so that they are not mixed in the synthetic light.
The components of the optical system including these reflection type light valves and polarization beam splitter were mounted individually on a mounting base, e.g. on a mounting base forming a floor member of a housing of the apparatus, thereby achieving the desired placement among the components. In other words, this conventional projection type display apparatus had the structure in which the components were fixed to each other through the mounting base and in which the positional relation among the components was determined through the mounting base. Materials for this mounting base were aluminum alloys, fiber reinforced resins, and so on, which were light in weight and had high workability.
This structure, however, had the problem of occurrence of so-called registration deviation that the base experienced elongation or distortion with change in the ambient temperature during operation to cause deviation of positional relation among the optical members, so as to alter positions of respective color pixels relative to each other on the screen. Particularly, in the case of the recent projection type display apparatus for projection onto a large screen, the registration deviation heavily degraded the projected image, which was a serious problem.
The present invention has been accomplished under the above-described circumstances and an object of the present invention is to provide an optical system for projection type display apparatus that can reduce the registration deviation, thereby improving the quality of projected image.
The inventors contemplated that the above registration deviation occurred as follows; the floor member on which the above-stated light valves, analyzing optical system, and color synthesizing optical system were fixedly mounted experienced expansion and contraction with change in the ambient temperature to change the positions of the components mounted thereon, so that the pixels of the respective colors deviated from their original positions achieved by initial positioning.
First of all, in order to decrease the expansion and contraction of the floor member due to the temperature change, a conceivable way is to select a material having a small thermal expansion coefficient for the floor member. In general, iron-based materials as a typical example of such material have a drawback of large weight and thus are not used easily. Further, nickel alloys typified by invar with small thermal expansion coefficient reveal poor workability and are very expensive.
The inventors considered that the above problem could be solved while using the conventional aluminum alloys or fiber reinforced resins as the material for the floor member, and accomplished the present invention.
As a result, the inventors found that the aforementioned registration deviation was reduced by integrally forming the optical system through which the modulated light beams emitted from the respective light valves traveled to be color-synthesized and outputted and that, further by fixing a member closest to the projection lens out of the thus integrated members to the floor member, focus deviation of projected image was also reduced in combination with the integration effect. This is because the change in distance with temperature change becomes ignorable when the distance is small between the fixed member and the projection lens fixed to the floor member.
The present invention provides an analyzing-synthesizing optical system unit for projection image display apparatus in which beams of the three primary colors of R, G, and B are modulated by respective, dedicated polarization beam splitters and light valves, the modulated beams are extracted, and a synthesizing optical system synthesizes the three color beams to output synthetic light, wherein the light valves and the polarization beam splitters are fixed as integrated with the synthesizing optical system and wherein optical path lengths of optical paths for the respective colors, established by each light valve, each polarization beam splitter, and the synthesizing optical system, are approximately equal to each other.
In this structure, the members constituting each optical path are integrated without intervention of the mounting base, so that the positional relation among the components is independent of the mounting base. With change in the ambient temperature, the relative positional deviation between the light valves will result from only deviation caused by dimensional change of the members including the light valves, polarization beam splitters, and so on, and is completely free of the expansion and contraction of the mounting base accordingly. Therefore, amounts of the deviation can be reduced remarkably when compared with the deviation due to the thermal expansion coefficient of the projection type display apparatus as in the conventional projection type display apparatus described above. Further, amounts of the deviation caused by the dimensional change of the members are almost equal because of the approximately equal path lengths, so that the effect thereof is further relaxed. Therefore, even if the material for the mounting base is selected from the aluminum alloys and the fiber reinforced resins with relatively large thermal expansion coefficients in view of the weight reduction, workability, and cost, the registration deviation can be reduced largely and the quality of projected image can be improved, as compared with the conventional projection type display apparatus.
The present invention also offers an optical system unit for projection image display apparatus in which incident white light is polarized and separated by a polarization beam splitter to be separated into beams of the three primary colors of R, G, and B by a separating-synthesizing optical system, the beams are modulated by respective, dedicated light valves, the modulated beams are synthesized again by the aforementioned separating-synthesizing optical system, and only the modulated light is extracted by the above polarization beam splitter, wherein the light valves and the polarization beam splitter are fixed as integrated with the synthesizing optical system and wherein optical path lengths of optical paths of the respective colors, established by each light valve and the separating-synthesizing optical system, are approximately equal to each other.
In this case, the separating optical system is also integrated, which is further preferable. This also has the effect of making the entire optical system compact.
When these optical systems are applied to the projection type display apparatus, the projection type display apparatus can be achieved with less registration deviation and less focus deviation. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.